For 99% of us, they are a 100% complete waste of $$$. The 1% it helps are those racing at the drag strip where it would make a very minor difference at wide-open throttle and near redline RPMs.
Around town, on the trail, and on the highway, you won't notice any difference. By law (smog laws), a chip can only change anything like advance the timing at wide-open throttle and near redline rpms. And once the chip is installed, the engine will ping in those conditions unless you run 89 or 91 octane.
I should add one more group might benefit... 16 and 17 year olds who haven't yet learned to drive except at wide-open throttle and near redline.